ABSTRACT: Sediment disturbance and transport on burned hillslopes in mountainous forests of Interior British Columbia, Canada.

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Abstract

Many western Canadian forests are susceptible to stand-replacing crown fires. Few studies on geomorphic effects of wildfire have considered post-fire erosional processes in western Canada. This project investigates hillslopes subjected to wildfire in eastern British Columbia, examining the integrated effects of biogenic and mechanical sediment disturbance and transport processes in the first two years following a crown fire. Although largely studied in temperate deciduous forests, biogenic sediment disturbance and transport through uprooting is an active hillslope process in mountainous coniferous forests. Upheaval of large amounts of sediment is readily observed on root-plates of uprooted trees. The effects of stand-replacing wildfire on the uprooting process, and the geomorphic contributions of this process to post-fire sediment production and transport, have not previously been investigated. After stand-replacing wildfire, tree topple rates are expected to increase due to the large numbers of fire-killed trees. Disintegration rates of pre-existing and new root-plates may be accelerated due to fire removal of the protective vegetation canopy. Uprooting thus provides an additional sediment source for transport by hillslope transport processes, such as overland flow or rainsplash. Previous studies have found increased rates of sediment movement by overland flow on post-fire hillslopes. The uprooting process, and soil exposure due to burning of the canopy and forest floor duff layer, provide a scenario for amplified downslope movement of sediment during the early post-fire seasons. Results from the study in Kootenay National Park, British Columbia are contrary to most post-fire studies and indicate very low sediment transport rates on the hillslopes. The study shows that uprooting is an important process in these forests, and provides a sediment source for subsequent sediment transport by overland flow. In addition, the land surface has had much of the protective duff layer removed by burning, facilitating rainsplash erosion and sediment transport by overland flow. However, hillslope erosion rates, as well as disintegration rates for root-plates and mounds, are dependent on weather patterns and storm intensities following the fire, and it appears that the threshold values of precipitation at this site have not been reached in the first two years after the fire occurrence.

Bibliography of Canadian Geomorphology